Apple Watch Vitals app can predict when you're going to be sick days in advance

As part of the updates in the watchOS 11 update, the Vitals app provides users with a quick reference point for their daily health. A month after its release, the feature is receiving praise from its users for detecting when they are about to be unwell.

Posts to Reddit have surfaced, with users noticing the Vitals app is notifying them of issues before they get sick. In one to r/AppleWatch, a user proclaims "The Vitals app knew I was sick 3 days before I did."

In the post, Redditor "dalethomas81" said they woke up feeling "off," and later in the evening they felt the "old familiar feeling in my head" of being sick. They accompany the brief post with a screenshot from Vitals on the iPhone, showing three outliers for high wrist temperatures in the three days prior.

Another post from "Vicari0" adds the Vitals app is "Spot on! Super useful feature!" Their image is of an Apple Watch Ultra showing three overnight outliers, again as proof of its predictableness.

The Vitals app is designed to collect and analyze a myriad of data points as the user sleeps. These include sleep data, their heart rate, respiratory rate, blood oxygen level, and skin temperature at rest.

In cases when multiple data points are away from the user's normal levels by too much, they are considered outliers, and the user is notified. The app doesn't outright tell users to go to a doctor or that they will be unwell, but advises that there are unusual readings that the user may want to act upon.